Bosch Mahle Turbo Systems–Two-stage turbocharging for commercial vehicle engines

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Two-stage turbocharger for commercial vehicles

The two-stage turbocharger from Bosch Mahle Turbo Systems allows the requirements for improved engine dynamics and lower emissions to be met.

Picture source: BMTS


Hanover, September 2012 – Due to the simultaneous demands for reduced pollutant emissions and increased effective overall efficiency, the ongoing development of future commercial vehicle engines presents a great challenge. Bosch Mahle Turbo Systems (BMTS) has therefore developed a controlled, two-stage turbocharging system that provides both a considerably higher charge air pressure level and increased dynamic response over the entire speed range. This is perceptible in the vehicle as a significant improvement in starting torque and transient response, while effective fuel consumption and emissions are reduced.

Since 2010, BMTS has been active in the field of exhaust gas turbocharging for commercial vehicle engines. The spread between the largest and smallest BMTS commercial vehicle turbochargers now covers turbocharged engines with displacements from 2.9 to 16 liters. In 2012, the model range will be completed, and all projects from light to heavy duty are covered—the intermediate range has now been filled in with projects as well.

Increasing requirements
As in the passenger car sector, legal requirements in the commercial vehicle area are continuously changing. In addition to stricter standards for nitrogen oxide and particulate emissions (and particle count as of 2013 with EURO VI) and the proportion of unburned or partially oxidized hydrocarbons, legal limits on effective fuel consumption are likewise under debate. Changes to the certification process, meaning new driving cycles and test conditions, also lead to new trends in the development of commercial vehicle engines.

Two-stage turbocharging
One key technology for achieving these challenging goals is the controlled two-stage exhaust gas turbocharging system developed by BMTS. It consists of two exhaust gas turbochargers of different sizes (high-pressure and low-pressure stages) connected in series, one after the other. At low engine speeds, the high-pressure stage provides a high pressure ratio with its small rotor, despite the low throughput rate. This manifests itself in a high starting torque and high combustion air ratio, which has a positive effect on soot and nitrogen oxide emissions.

In contrast to single-stage turbocharging, the low moment of inertia of the rotor in the high-pressure stage also provides a significantly faster rise in charge air pressure. This results in considerably faster torque production when starting or shifting gears.

As the engine speed increases, part of the increasing exhaust gas mass flow is shunted to the low-pressure stage by means of a bypass valve. On the compressor side, the air fed to the engine is first precompressed in the low-pressure stage, and then the pressure ratio is increased further in the high-pressure stage. In order to protect against thermal overloading of the high-pressure compressor and to increase the overall efficiency, effective charge air cooling is employed between the two stages.

With efficient controls and utilization of the two different turbocharging stages, significantly higher charge air pressure and more efficient gas exchange are achieved simultaneously over the entire engine operating map. This has a positive effect on the total emissions, full-load torque curve, transient operation, and above all the effective fuel consumption.

About BMTS
Founded in 2008, Bosch Mahle Turbo Systems is a joint venture of Bosch and MAHLE—two well-known parent companies with rich traditions, both representing high standards and top quality. Bosch Mahle Turbo Systems develops and produces tailor-made exhaust gas turbochargers for passenger cars and commercial vehicles. The company currently employs around 350 people at locations in Stuttgart and Blaichach in Germany, and St. Michael in Austria.

Press contact at MAHLE GmbH:
Ruben Danisch
Pragstrasse 26–46
70376 Stuttgart
Phone: +49 711 501-12199
Fax: +49 711 501-13700